Rotary coating apparatus having a bell cup applicator for applying coatings to workpieces is known in the art, and known to be driven by compressed air actuated turbines. Such bell cup applicators are used in operations wherein liquid based paint is atomized at the outer edge of the spinning cup and sprayed onto the workpiece, as well as in similar operations wherein powder coatings are applied directly to the substrate.
Electrical charges are often applied to the coating particles to enhance adherence to the grounded workpiece. Cups can rotate from 10,000 to upwards of 70,000 rpm and, owing to such high speeds, the cups must be mounted on their drive shafts with extreme precision in order to minimize radial load imbalances in operation.
Coating operations are typically carried out robotically. In operation at high speeds, the coating material, for various reasons, can back up into unintended areas of the rotary drive mechanisms and onto the workpiece being coated, possibly causing imperfections in the coating and/or downtime in the coating operation, all of which are undesirable events. To counter and minimize such events, auxiliary apparatus is generally provided whereby a solvent cleaning fluid can periodically be caused to pass through and over the bell cup and various parts of the coating apparatus in order to clean them.
It is also known in prior art coaters to provide a cylindrically shaped curtain of air, termed “shaping air”, about the spinning bell cup during the coating process, which directs the coating particles toward the workpiece and controls the diameter and pattern of the sprayed particles. To provide this curtain of shaping air, it is known to include a plurality of shaping air orifices through the shroud over the turbine which are concentric with the bell cup, adjacent the outside surface thereof. Shaping air is routed to and into the shroud between the shroud and the turbine and, in some instances, through openings in the bearing or bearing retainer supporting the turbine, and/or through spaces between the turbine housing and the bearing retainer, and back into the turbine housing before passing to and outwardly through the shaping air orifices, thereby forming a generally cylindrical curtain about the rotating cup.
The foregoing briefly and generally describes the state of the art and the basic principles relating to the invention described and claimed herein, and these will not be repeated below. For specific prior art references describing such apparatus, reference may be had to U.S. Pat. Nos. 5,397,063; 7,036,750B2 and 7,131,601 B2.